My 2-cents analogy for Dark Wallet:
About 15 years ago, I was exposed to several radical start-ups in Israel in the fields of betting and forex.
At the time, html looked pale, whereas Flash was really pushing the limits in user experience, animation, etc.
It took time to understand an apparent paradox-
People liked very much the betting and financial presentation of markets in Flash, but apparently where not loading money to their account. At the time, the general thought was it's because people are afraid to give their credit-cards or don't trust the companies...
It took some time until the 'dime fell'. The reason was that people where not trusty of Flash as means to transfer their credit-card details. It was too shinny. Like a honeypot...
When 2 groups of people were offered the choices - an html page for entering their credit-card details (with a secure https lock etc.), or a Flash interface, the numbers were overwhelmingly favorable to html.
Fast forward to 2014 - Dark Wallet:
From the little I understand, DarkWallet is a plugin for browsers...
I believe people do not trust plug-ins with their money, in the same manner as they did not trust flash.
To strengthen my argument above, I can stress that I've seen more than a few start-ups in the past decade that deal in NFC (Near Field Communications), and other types of mobile payments and eCash. Al have failed... and it wasn't because of the technology.